cruise control gremlins
 

Cruise control generally works but will cut off when climbing a hill. Without a load, it won't malfunction at cruise speeds below 80mph. At 70-75 it will go up the hill just fine it seems. The cruise speed is steady, but at 80 it will reach a certain throttle position (i think) and just quit. The cruise light will stay on but it won't function again until the truck is turned off and on again.

Thinking it may be a faulty brake light switch, I jiggled the brake pedal around (every direction but down) with cruise on trying to set it off but that wouldn't do it.

Last week, I had about a 5k pound load, trailer included, and I was cruising at 60mph with no problem up and down hills (by hills I mean overpasses, there aren't really hills here). Then I slowed to 55mph (below 1500rpm for me) and on the way up a hill, it quit again.

I'm thinking it has to do with fuel consumption. Any ideas?

Probably the vacuum pump and or vacuum leak on one of the lines. Pump is located next or under the passenger side battery. The early 3rd gens with auto used a vacuum pump for the cruise control.

how hard to add cruise control to my truck its a 3/4 6.7 diesel?

My pickup did this intermittently when I first got it,and became frequent the more I drove on highway. It always let go pulling a hill. Found a vacuum line had a hole rubbed in it near the oil dipstick. I used a similar size wire splice connector and silicon. Never a cruise control issue since. That was nearly eight years ago